1. Field of the Invention
The present invention relates to an onboard apparatus and a train-position calculation method for calculating a train position.
2. Description of the Related Art
There has conventionally been known an onboard-oriented train control device that subjectively manages a rail track position of a train and controls a train speed. The onboard-oriented train control device has GPS antennas and GPS receivers that are arranged in a distributed manner in a train constituted by a plurality of railway vehicles, and includes a storage device that stores therein route maps and GPS-antenna installation position information, so as to improve the reliability of detection of the train position. The onboard-oriented train control device performs positioning calculation by causing each GPS receiver to receive GPS signals from at least four satellites, and recognizes rail track position and direction of the entire train with using the route maps. Japanese Patent Application Laid-open No. 2004-168216 discloses such a technique.
However, according to the above conventional technique, because the train position is corrected in association with the route maps using the GPS signals at any time, when a train continues running in a non-received state of the GPS signals, a break is outputted to stop the train after running a specified distance, for the reason that the train position can not be surely located. Therefore, in a section where reception of the GPS signal is difficult because of the geographical reasons such as tunnels, valleys, places surrounded with buildings, even if any GPS signals can not be received momentarily during the section or near the section, a break may be outputted and the train may stop.